Organic semiconductor element

ABSTRACT

An organic semiconductor element functions as a strain sensor, and includes a substrate and an organic semiconductor layer formed on the substrate as a single-crystal thin film of an organic semiconductor that is a polycyclic aromatic compound with four or more rings or a polycyclic compound with four or more rings including one or a plurality of unsaturated five-membered heterocyclic compounds and a plurality of benzene rings. Since the organic semiconductor layer is formed as the single-crystal thin film, an identical crystal structure is obtained regardless of formation technique. Therefore, when the same strain is given, the same carrier mobility is obtained and uniform property is obtained with respect to the strain. Accordingly, it is possible to provide strain sensors having uniform property.

This is a divisional of application Ser. No. 15/547,594 filed Jul. 31,2017, which is a National Stage Application of PCT/JP2016/052266 filedJan. 27, 2016, which claims the benefit of JP 2015-015744 filed Jan. 29,2015. The entire disclosures of the prior applications are herebyincorporated by reference herein their entirety.

TECHNICAL FIELD

The present disclosure relates to an organic semiconductor element.

BACKGROUND

Conventionally, as an organic semiconductor element of this type, therehas been proposed an organic semiconductor element in which acompressive stress is applied to a multi-crystal or amorphous organicsemiconductor (see Patent Literature 1, for example). In this device,the organic semiconductor is formed as a thin film on a bent substrateby a vapor deposition or a spin coating, and the compressive stress isapplied to the organic semiconductor by stretching the bent substrateuntil the substrate becomes planar. With the compressive stress appliedto the organic semiconductor, the carrier mobility of the organicsemiconductor is increased.

CITATION LIST Patent Literature

-   PTL 1: JP2005-166742

SUMMARY

However, in the above-described organic semiconductor element, since amulti-crystal or amorphous organic semiconductor is used, it isdifficult to obtain organic semiconductors having an identicalmulti-crystal structure or an identical amorphous structure. Because ofthe difference in the structure, even when organic semiconductors areproduced by the same technique and the same compressive stress isapplied so that the same strain is given, the organic semiconductorsoften differ in the carrier mobility, and it is difficult to obtainorganic semiconductor elements having uniform property.

A primary object of an organic semiconductor element in the presentdisclosure is to provide organic semiconductor elements having uniformproperty.

For achieving the above-described primary object, an organicsemiconductor element in the present disclosure adopts the followingconfigurations.

In the organic semiconductor element in the present disclosure, theorganic semiconductor element includes an organic semiconductor. Theorganic semiconductor is formed as a single-crystal thin film, and theorganic semiconductor element operates based on carrier mobility when astrain is given to at least the organic semiconductor.

In the organic semiconductor element in the present disclosure, theorganic semiconductor is formed as the single-crystal thin film. Thecrystal structure of a single crystal is determined by the molecules,and therefore, basically, an identical crystal structure is obtainedregardless of the production technique. Therefore, when the same strainis given, the same carrier mobility can be obtained. Accordingly, it ispossible to obtain organic semiconductor elements having uniformproperty.

Here, the organic semiconductor may be formed as a thin film whosethickness is 200 nm or less, for example, 100 nm or 50 nm. It ispreferable that the strain to be given to the organic semiconductor bein a range of 10% or less in a compression direction. Further, as theorganic semiconductor, the organic semiconductor may be composed of apolycyclic aromatic compound with four or more rings, or a polycycliccompound with four or more rings including at least one unsaturatedfive-membered heterocyclic compound and a plurality of benzene rings.

In the organic semiconductor element in the present disclosure, theorganic semiconductor may be kept in a state where a predeterminedstrain is applied in a movement direction of carriers. That is, theorganic semiconductor is used while the carrier mobility is fixed in thestate where the predetermined strain is applied. By using such anorganic semiconductor, it is possible to obtain various semiconductordevices.

In the organic semiconductor element in the present disclosure, theorganic semiconductor element may be operated based on mobility ofcarriers when a predetermined strain as a standard is given to theorganic semiconductor and carrier mobility when a different strain fromthe predetermined strain is given to the organic semiconductor. Thereby,it is possible to use the organic semiconductor element as a sensordevice.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram showing an exemplary configuration ofan organic semiconductor element 20 according to a first embodiment ofthe present disclosure;

FIG. 2 is an explanatory diagram showing an example of how an organicsemiconductor layer 30 is formed;

FIG. 3 is a schematic diagram schematically showing the view of thecrystal structure of the organic semiconductor layer 30, as viewed fromthe b-axis direction;

FIG. 4 is a schematic diagram schematically showing the view of thecrystal structure of the organic semiconductor layer 30, as viewed fromthe a-axis direction;

FIG. 5 is an explanatory diagram showing a relation between mobility ofcarriers and magnitude of a strain in the organic semiconductor layer30;

FIG. 6 is a schematic diagram schematically showing how moleculesvibrate before and after a compressive stress is applied to asingle-crystal organic semiconductor;

FIG. 7 is an explanatory diagram showing an exemplary configuration ofan organic semiconductor element 120 according to a second embodiment ofthe present disclosure; and

FIG. 8 is an explanatory diagram showing an exemplary formation methodfor an organic semiconductor layer 130.

DETAILED DESCRIPTION OF EMBODIMENTS

The following describes some aspects of the disclosure with reference toembodiment.

FIG. 1 is an explanatory diagram showing an exemplary configuration ofan organic semiconductor element 20 that functions as a strain sensoraccording to a first embodiment of the present disclosure. The organicsemiconductor element 20 includes a substrate 22, an organicsemiconductor layer 30 formed on the substrate 22, and two gauge leads32 formed on the organic semiconductor layer 30 (one of the two gaugeleads 32 is not illustrated).

The substrate 22 is formed of a plastic (for example, polyethylenenaphthalate), such that the thickness is 50 μm to 10 mm, for example,100 μm to 200 μm.

The organic semiconductor layer 30 is formed such that the thickness is200 nm or less, for example, 100 nm or 50 nm, as a single-crystal thinfilm of an organic semiconductor (for example, 3,11-didecyldinaphto[2,3-d:2′,3′-d′]benzo [1,2-b:4,5-b′]dithiophene (C10-DNBDT) having astructure shown in the following Formula (1)).

Here, a formation method for the organic semiconductor layer 30 will bedescribed. FIG. 2 is an explanatory diagram showing an example of howthe organic semiconductor layer 30 is formed. First, a blade 50 isarranged above the substrate 22, so as to be nearly perpendicular to thesubstrate 22. At this time, the blade 50 is arranged such that thedistance between the substrate 22 and a tip 50 a of the blade 50 is apredetermined distance (for example, 200 μm) that is greater than thethickness of the organic semiconductor layer 30 to be formed. Then,while a solution 54 in which the organic semiconductor is dissolved inan aromatic compound (for example, o-dichlorobenzene) as a solvent issupplied to the gap between the substrate 22 and the tip 50 a of theblade 50 from the left side in FIG. 2 using a solution supply pipe 52,the substrate 22 is slowly moved in the right direction in the figure.Thereby, the solvent of the solution 54 at a portion away from the tip50 a of the blade 50 evaporates, so that the organic semiconductor layer30 is formed as a single-crystal thin film. At this time, by matchingthe movement speed of the substrate 22 with the growth speed of thesingle crystal, it is possible to grow the single crystal from a growthpoint 56 in FIG. 2, such that the single crystal has a uniformthickness. Here, in the embodiment, the substrate 22 is moved in theright direction in the figure, but the blade 50 and the solution supplypipe 52 may be moved instead of the movement of the substrate 22.

FIG. 3 is a schematic diagram schematically showing the view of thecrystal structure of the organic semiconductor layer 30, as viewed fromthe b-axis direction, FIG. 4 is a schematic diagram schematicallyshowing the view of the crystal structure of the organic semiconductorlayer 30, as viewed from the a-axis direction, and FIG. 5 is anexplanatory diagram showing a relation between carrier mobility andmagnitude of a strain in the organic semiconductor layer 30. In FIGS. 3and 4, the three crystal axes (the a-axis, the b-axis and the c-axis)are shown by arrows, and a unit cell is surrounded by a quadrangle. Inthe organic semiconductor layer 30, for example, when a compressivestress is applied in the direction (the direction shown by the broadarrows in FIG. 3) parallel to the c-axis in the crystal structure of theorganic semiconductor and a strain is given to the organic semiconductorlayer 30, the carrier mobility changes depending on the magnitude of thegiven strain, as shown in FIG. 5. The carrier mobility is determineddepending on the magnitude of the strain to be given, and increases asthe strain to be given increases. For example, the carrier mobility whenthe strain is 3% is 16.5 [cm²/(V·s)], which is 1.7 times the carriermobility when the strain is 0%. Generally, multi-crystal organicsemiconductors differ in crystal structure, depending on the formationtechnique. Therefore, even when the same compressive stress is appliedand the same strain is given, it is not possible to obtain the samecarrier mobility. In contrast, in single-crystal organic semiconductors,the crystal structure is determined by the molecule. Therefore,basically, an identical crystal structure is obtained regardless of theformation technique, and it is possible to obtain the same carriermobility when the same compressive stress is applied and the same strainis given. Therefore, the single-crystal organic semiconductors haveuniform property with respect to the strain. As the reason for theincrease in the carrier mobility, the following reason is conceivable.FIG. 6 is a schematic diagram schematically showing how moleculesvibrate before and after a compressive stress is applied to thesingle-crystal organic semiconductor. When the compressive stress isapplied to the single-crystal organic semiconductor, it is thought thata strain occurs to the crystal, molecules come closer to each other andthe movement of the carrier in the organic semiconductor becomes easierso that the carrier mobility increases. Further, when molecules comecloser to each other, the vibration of molecules becomes smaller.Therefore, it is thought that after the compressive stress is applied,as illustrated, the vibration of molecules becomes smaller, the movementof the carrier in the organic semiconductor becomes easier and thecarrier mobility increases, compared to before the compressive stress isapplied. Furthermore, the distance among molecules becomes closer as thestrain to be given to the crystal increases, and therefore, the carriermobility increases as the strain to be given to the crystal increases.Thus, the single-crystal organic semiconductor has a property ofincreasing the carrier mobility as the strain to be given increases, andthis property is consistent regardless of the formation technique forthe organic semiconductor. In the embodiment, since the organicsemiconductor layer 30 is formed as the single-crystal thin film, theorganic semiconductor layer 30 can have uniform property with respect tothe strain (the property of increasing the carrier mobility as thestrain to be given increases).

In the organic semiconductor element 20 configured in this way, themagnitude of the strain of an object is detected, in the followingprocedure. First, a predetermined voltage is applied to the gauge leads32 in a state where the substrate 22 sticks with the object to bedetected. When the strain of the object to be detected changes, thestress to be applied to the organic semiconductor layer 30 together withthe substrate 22 changes, and the strain to be given to the organicsemiconductor layer 30 changes. When the strain to be given to theorganic semiconductor layer 30 changes, the carrier mobility in theorganic semiconductor layer 30 changes depending on the magnitude of thestrain, and the gauge current to flow through the gauge leads 32changes. In the organic semiconductor element 20, by measuring thechange in the gauge current, it is possible to measure the magnitude ofthe strain of the object to be detected. Further, the organicsemiconductor layer 30, which is formed as the single-crystal thin film,has uniform property with respect to the strain, and therefore, it ispossible to provide strain sensors having uniform property.

According to the above-described organic semiconductor element 20 in thefirst embodiment that functions as a strain sensor device, since theorganic semiconductor layer 30 is formed as the single-crystal thinfilm, it is possible to measure the magnitude of the strain of thedetection target. Further, since the organic semiconductor layer 30 isformed as the single-crystal thin film, it is possible to obtain thesame carrier mobility when the same strain is given, and it is possibleto provide strain sensors having uniform property.

In the first embodiment, the organic semiconductor element 20 functionsas a strain sensor. However, the organic semiconductor element 20 is notlimited to elements that function as a strain sensor in this way, andmay be used as any element that operates based on the carrier mobilitywhen the strain changes (the carrier mobility when a predeterminedstrain as the standard is given and the carrier mobility when adifferent strain from the predetermined strain is given), as exemplifiedby a pressure sensor that detects the pressure given to a pressuresensitive part, and a temperature sensor that detects temperature. Forexample, in the case of the use as a pressure sensor, the organicsemiconductor element may be stuck to a sheet, and based on the current(the carrier mobility) that flows when the strain of the organicsemiconductor element changes by the press of the sheet, the pressuregiven to the sheet may be detected. Further, in the case of the use as atemperature sensor, the organic semiconductor element may be bonded tometals having different thermal expansion coefficients similarly to abi-metal, and based on the current (the carrier mobility) when thestrain of the organic semiconductor element changes due to thedifference in thermal expansion coefficient caused by the change intemperature, the temperature may be detected.

Next, an organic semiconductor element 120 in a second embodiment thatfunctions as a transistor will be described. FIG. 7 is an explanatorydiagram showing an exemplary configuration of the organic semiconductorelement 120 according to the second embodiment of the presentdisclosure. The organic semiconductor element 120, which is configuredas a top contact-bottom gate type field-effect transistor, includes asubstrate 122, a gate electrode 124 formed on a predetermined region ofthe substrate 122, a gate insulating film 126 formed on the substrate122 and the gate electrode 124, an organic semiconductor layer 130formed on the gate insulating film 126 so as to be positioned above thegate electrode 124, and a source electrode 132 and drain electrode 134formed on the gate insulating film so as to be positioned on both sidesof the organic semiconductor layer 130.

The substrate 122 is formed of a plastic (for example, polyethylenenaphthalate), such that the thickness is 50 μm to 10 mm, for example,100 μm to 200 μm.

The gate electrode 124, the source electrode 132 and the drain electrode134 are formed of a metal material such as gold. The gate electrode 124is formed such that the thickness is 50 nm or less, for example, 40 nmor 30 nm. The source electrode 132 and the drain electrode 134 areformed such that the thickness is 50 nm or less, for example, 40 nm or30 nm.

The gate insulating film 126 is formed of an insulating material (forexample, polymethyl methacrylate), such that the thickness is 200 nm orless, for example, 150 nm or 100 nm.

The organic semiconductor layer 130 is formed such that the thickness is200 nm or less, for example, 100 nm or 50 nm, as a single-crystal thinfilm of an organic semiconductor having the above-described structureshown in Formula (1). The organic semiconductor layer 130 is formed suchthat the c-axis of the crystal axes in the crystal structure shown inFIG. 3 is parallel to the orientation of a channel to be formed, and iskept in a state where a predetermined strain is applied by applying acompressive stress in the c-axis direction. Here, the “predeterminedstrain” only needs to be a strain by which the organic semiconductorlayer 130, the substrate 122 or the gate insulating film 126 is notbroken, and in the embodiment, a strain of 10% or less in thecompression direction, for example, a strain of 3% in the compressiondirection can be used.

Here, a formation method for the organic semiconductor layer 130 will bedescribed. FIG. 8 is an explanatory diagram showing an exemplaryformation method for the organic semiconductor layer 130. First, asillustrated, a single-crystal thin film of the organic semiconductor(the organic semiconductor layer 30) is formed in the right-leftdirection in the figure, in a state where the substrate 122 having thegate insulating film 126 formed is bent. Thereafter, the substrate 122is stretched until the substrate 122 becomes planar, and the compressivestress is applied to the thin film. Thereby, the organic semiconductorlayer 130 kept in the state where the predetermined strain is applied isformed. As the method for keeping the organic semiconductor layer 130 ina state where a predetermined strain is applied, other than the methodexemplified in FIG. 8, it is allowable to use another method such as amethod of forming a single-crystal thin film of the organicsemiconductor in a state where the substrate 122 is heated and isthermally expanded and thereafter thermally contracting the substrate122 at normal temperature.

Since the organic semiconductor layer 130 is formed as thesingle-crystal thin film in this way, it is possible to obtain the samecarrier mobility when the same compressive stress is applied to and thesame strain is given to the organic semiconductor layer 130.Accordingly, the organic semiconductor layer 130 can have uniformproperty with respect to the strain.

The organic semiconductor element 120 configured in this way operates asa transistor, when a channel is formed in the organic semiconductorlayer 130 by applying voltages for operation to the gate electrode 124,the source electrode 132 and the drain electrode 134 respectively. Theorganic semiconductor layer 130, which is formed as the single-crystalthin film, has uniform property with respect to the strain, andtherefore, it is possible to provide transistors having uniformproperty. Further, since the organic semiconductor layer 130 is kept inthe state where the strain is applied, the carrier mobility is highercompared to when the strain is not applied. Therefore, it is possible tomake a larger current flow between the source electrode 132 and thedrain electrode 134, and it is possible to provide a transistor having ahigher drive power.

According to the above-described organic semiconductor element 120 inthe second embodiment that functions as a transistor, since the organicsemiconductor layer 130 is formed as the single-crystal thin film, it ispossible to provide a transistor having a high drive power. Further,since the organic semiconductor layer 130 is formed as thesingle-crystal thin film, it is possible to obtain the same carriermobility when the same strain is given, and it is possible to providetransistors having uniform property.

In the second embodiment, the organic semiconductor element 120 isconfigured as a top contact-bottom gate type field-effect transistor,but may be configured as any type of transistor that can be formed on aninorganic semiconductor such as silicon and gallium nitride, asexemplified by a top contact-top gate type field-effect transistor.Further, the organic semiconductor element is not limited to suchtransistor, and may be used as any element that can be kept in a statewhere a predetermined strain is applied in the movement direction of thecarrier.

In the organic semiconductor elements 20, 120 in the first and secondembodiments, the organic semiconductor layers 30, 130 are formed of theorganic semiconductor having the above-described structure in Formula(1). However, as the organic semiconductor, for example, a polycyclicaromatic compound with four or more rings or a polycyclic compound withfour or more rings including one or a plurality of unsaturatedfive-membered heterocyclic compounds and a plurality of benzene ringscan be used. For example, any structure in the following Formula (2) toFormula (14) may be adopted. In Formula (2) to Formula (14), as R, astraight alkyl, a branched alkyl, a fluorinated straight/branched alkyl,triisopropylsilylethynyl, phenyl or the like can be used.

There may be many other modifications, changes, and alterations withoutdeparting from the scope or spirit of the main characteristics of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure can be utilized in production industries for anorganic semiconductor element, and the like.

The invention claimed is:
 1. An organic semiconductor element comprisesan organic semiconductor, wherein the organic semiconductor is formed asa thin film of single-crystal composed of a polycyclic compound withfour or more rings including at least one unsaturated five memberedheterocyclic compound and a plurality of benzene rings, at least onebenzene ring is arranged on both sides of the unsaturated five memberedheterocyclic compound, the organic semiconductor has band conductivitybeing a carrier transfer mechanism in high mobility organicsemiconductor having mobility of carrier greater than or equal to 9.7cm²/Vs, the organic semiconductor element operates based on mobility ofcarrier when a strain is given to at least the organic semiconductor,and the organic semiconductor is kept in a state where a strain isapplied in a movement direction of carriers.
 2. The organicsemiconductor element according to claim 1, wherein the thin film ofsingle-crystal has a unit cell with an a-axis, a b-axis and a c-axis,the c-axis being orthogonal to a direction in which layers of thepolycyclic compound are stacked in the thin film of single-crystal, theorganic semiconductor is kept in the state where the strain is appliedby applying a compressive stress in the direction parallel to the c-axisof the unit cell of the thin film of single-crystal.
 3. The organicsemiconductor element according to claim 2, further comprising: a gateelectrode; a source electrode; and a drain electrode, wherein the gateelectrode is arranged in the a-axis direction of the unit cell of thethin film of single-crystal via a gate insulating film, the a-axisdirection being parallel to the direction in which layers of thepolycyclic compound are stacked in the thin film of single-crystal, andthe source electrode and drain electrode are arranged so as to bepositioned on both sides of the organic semiconductor in the c-axisdirection of the unit cell of the thin film of single-crystal.
 4. Theorganic semiconductor element according claim 1, wherein the organicsemiconductor is formed as a thin film having a thickness of 200 nm orless.
 5. The organic semiconductor element according to claim 1, whereinthe strain to be given to the organic semiconductor is in a range of 10%or less in a compression direction.